Spray Backstop

Spray Backstop - developed at UC Davis digital Ag lab - Alireza Pourreza
Spray Backstop is a low maintenance attachment system for air-assist sprayers that blocks the spray droplets escaping the canopy from tree's top or sides. 

Principal Investigator: Alireza Pourreza

Project Sponsor: Almond Board of California

Collaborators: Ali Moghimi, German Zuniga-Ramirez, Bruno Batista da Silva, Franz Niederholzer, Peter Larbi

 

One of the major issues in almond pesticide application is spray drift while assuring good coverage, particularly on treetops. Unmanaged spray drift contributes to the environmental contamination, and it may also result in increased regulation of pest control activities. Additionally, offside movement of spray droplets causes a significant danger to farm workers, nearby residential areas, and off-target crop. Therefore, controlling spray drift becomes a high priority for growers.

UC Davis Digital Agriculture Lab Photo - Off-target movement of spray cloud during a spray event in a young almond orchard in northern California, fall 2018.
Off-target movement of spray cloud during a spray event in a young almond orchard in northern California, fall 2018.​​

In this project, we designed and fabricated the first prototype of a spray backstop system. This system includes a mast and a screen structure that covers the trees and blocks the spray droplets escaping from treetops. To evaluate spray drift reduction with the backstop system, we used a mixture of water and Fluorescent dye to spray an almond orchard with and without the spray backstop. A continues loop ribbon system was used to capture all off-target droplets scaping from top and sides. Leaf samples were also collected from the treetops located on both sides of the row and from two sides of trees (near and far). Cuts of the ribbon and leaf samples were analyzed in laboratory to quantify dye deposition. The results showed an overall reduction of 78% in airborne drift when the backstop system was used compared to spraying with the same setting but without the backstop. Although this prototype was not designed to provide drift reduction from the sides, a fair drift reduction of 47% from sides was observed as well. The laboratory analysis showed that leaves on treetops received 9% better spray deposition when spray backstop was used. These results clearly proved the effectiveness of spray backstop in reducing airborne drift and improving coverage on treetop.

Achieved Objectives

  1. The spray cloud movement was determined by monitoring aerial RGB and thermal views of an almond orchard spray operation with standard setting.
  2. The first prototype was designed and fabricated for young almond orchards based on the knowledge about how spray cloud moves from the first objective. The fabrication was conducted at the BAE shop. The prototype was test-assembled in Davis and then transferred to Nickels Soil Lab for on-site test.
  3. The spray drift reduction and coverage improvement in treetops were quantified by dye deposition analysis method.  A sprayer was filled with a mixture of water and Fluorescent dye and used to spray an almond orchard. Drift evaluation was performed using continuous loop sampling method with and without the backstop system. The experiments were conducted at the Nickels Soil Lab.

Monitoring spray cloud movement

In October 2018, an unmanned aerial system was used to capture thermal and RGB images and videos of the spray cloud movement from multiple direction to the sprayer.

UC Davis Digital Agriculture Lab Figure - Positions of aerial imaging system for monitoring spray cloud movement; a. 3D view; b. vertical view; c. horizontal view
Positions of aerial imaging system for monitoring spray cloud movement; a. 3D view; b. vertical view; c. horizontal view.

Two types of imagery from 3 different views. The aerial imagery was analyzed and the pattern of spray cloud movement in a young almond orchard was determine. The results were used in the design of the structure and size of the first prototype of spray backstop system.

 

Spray Backstop

The backstop system includes a foldable mast structure powered by the tractor hydraulic system. The height of the backstop was about six meters from ground at the upright position. To block the spray droplets escaping from trees tops, two waterproof tarps, with 8-millimeter thickness and 12x12 weave, were used for each side of the sprayer. It had grommets located every 18 inches, which were used for tying the tarp to the backstop. The width and total length of the screen was about 2 meter and 10 meters, respectively.

 

Field experiments

The orchard used for this experiment was planted in 2009 (11th leaf) and located at the Nickels Soil Lab. Rootstock was Lovell peach seedling. the following setup was used for spraying the almond orchard:

  • Forward speed of tractor: 2 MPH
  • System pressure: 160 psi
  • Nozzles: Spray Systems TXR80049VK; 4 nozzle per side; 0.971 gpm/nozzle, 3.88 gpm/side of sprayer.

Fluorescent dye (Pyranine) was mixed with water in the sprayer tank (approximately 54g of tracer with 130 gallons of water). The effectiveness of the backstop system in blocking drift was evaluated by a continuous loop sampling method in which a one inch cotton ribbon was stretched above the trees and on the rows adjacent to the row that was sprayed with and without the backstop system. Cotton ribbon was cut at 60 cm/piece. Top section had 23 samples and side sections (right/left) had 12 samples each. To evaluate the impact of the spray backstop on the spray converge, leaf samples were collected form the treetops on both sides of the sprayer. Sampling was done from two sides of each tree: the side near the sprayer and the side farther away from the sprayer. The ribbon and leaves samples were placed in pre-numbered bags, marked with the sample location in the continuous loop, and shipped to the UC Kearney REC for assessment of fluorescent dye deposition. Samples were analyzed by fluorometry technique at Dr. Peter Larbi’s lab located at Kearney REC, Parlier, CA.

Evaluation with Aerial imaging

For visual assessment of the spray cloud movement, aerial photos/videos were captured during the experiments. A DJI Mavic 2 Pro equipped with a 20MP camera was used for aerial imagery. Figure bellow shows the aerial images captured during the spraying and how the spray cloud lifted the ribbon from the rest position (compare Figure A and B). Alternatively, the ribbon remained in its rest position (Figure C) while using the backstop since the cloud was captured under the tarp. A comparison between Figure B and C shows how the backstop system effectively blocks the spray droplets that pass treetop and pushing them back to treetops. This observation was validated by the dye deposition results.

UC Davis Digital Agriculture Lab Photo - Aerial images captured from DJI Mavic drone. (A) it demonstrates the rest position of the ribbon, (B) it shows how cloud of droplets could lift the ribbon, mostly the left side, (C) it shows the backstop system could capture the cloud and therefore the ribbon remained in its rest position.
Aerial images captured from DJI Mavic drone. (A) it demonstrates the rest position of the ribbon, (B) it shows how cloud of droplets could lift the ribbon, mostly the left side, (C) it shows the backstop system could capture the cloud and therefore the ribbon remained in its rest position.

 

Results

The analysis of dye deposition on the ribbon samples at top and sides of the sprayer demonstrated a significant reduction in drift potential, largely from the top of the trees. Figure bellow shows the result of the dye deposition on the ribbon. With the backstop system, an average drift reduction of 78% at the top was measured comparing to spraying without the backstop system. Drift potential from the sides is a function of the target canopy size and foliage density. Using the spray backstop system caused an overall side drift reduction of 47%, including 26% reduction from the left side and 58% reduction from the right side. The pattern of dye deposition on ribbon indicated more drift from right and top-right sides that may suggest there was a wind from left to right during the test.

Results of dye deposition analysis without backstop and with backstop. The backstop system significantly reduced spay drift largely from the top of the trees
Results of dye deposition analysis without backstop and with backstop. The backstop system significantly reduced spay drift largely from the top of the trees.

Figure bellow illustrates dye deposition on leaves located on top one-third of the trees at the near side and far side of the target trees. Overall, deposition at treetops was improved by 9% when backstop was used. Since the backstop effectively blocks the scaping droplets, sprayers can be calibrated for more air and fine droplets to further improve overall deposition with no concern of drifting.

Results of dye deposition on leaves located on near and far side of the trees on both sides of the row. a) location of trees where the leaf samples were collected; b) Spray deposition results on the left side of the row; c) Spray deposition results on the right side of the row
Results of dye deposition on leaves located on near and far side of the trees on both sides of the row.

Conclusion

The main goal of this proposal was to develop a spray attachment system that improves the performance of air-assist sprayers in Almond, primarily by reducing spray drift. The first prototype of Spray Backstop system developed in this project was able to successfully block the spray cloud that passes the treetops and prevent them from escaping the orchard and becoming drift. Using the Spray Backstop system will allow growers to continue to adjust sprayers with more air and fine droplets that improves spray coverage in the hard-to-reach upper canopy area, while helping manage drift.

 

 

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